Some benefits of performing unilateral exercises:
Has an extremely good carryover to sports specific movements and everyday activities - Most movements that occur during sports and daily living involve one limb. Some examples include sprinting, planting, lunging, jumping, tackling, kicking, and striding.
Improves balance and stability - Many people make the mistake of trying to improve their balance and stability by training on unstable surfaces. The most effective strategy to improve your balance and stability is to perform unilateral exercises and on a stable surface. If more people were aware of this, the Bosu and wobble board producing companies would have gone bankrupt a long time ago!
Recruits more stabilizer muscles than bilateral exercises - A great example is the Bulgarian split squat and the glute medius muscle. While you will rarely feel this muscle working during a bilateral exercise like a squat or deadlift, you will definitely feel your glutes during (and especially after) performing Bulgarian split squats (assuming your glute meds are working properly). Once again, you will target your smaller ''stabilizer'' muscles much more effectively by performing unilateral exercises than you will flailing about like a fish out water on a Bosu or wobble board.
Helps prevent injuries - Many injuries occur because there is an imbalance in strength (and often mobility) between limbs. In some instances, the stronger limb will compensate for the weaker limb, and is often the area that will experience the pain/symptoms. Unilateral training will help prevent these imbalances from occurring and will make the body more resistant to injury. Training each limb independently will also help ensure that the mobility is similar on both sides of the body. This will help improve performance, and will decrease the risk of injury.
Allows you to train around injuries -When you are suffering from an injury, you can often improve your strength with single-legged exercises while avoiding the more stressful bilateral exercises. This is especially useful if you have sustained a back injury and are required to avoid the more spine-stressing exercises like back squats and deadlifts. Also, if you are injured and are not able to train one limb, many studies have shown that performing strength training exercises on the opposite limb will help slow down muscle atrophy and strength loss on the injured side.
Improves your ability to perform compound exercises - While this is fairly straightforward, performing single leg exercises will have a positive carryover effect to your double leg exercises. If you want to improve your ability to squat, deadlift, etc., add in some single leg squatting/lunging movements and single leg deadlifts, and you will notice a positive transfer to your regular squats and deadlifts.
Improves symmetry (address imbalances) - From an aesthetic standpoint, performing unilateral exercises will help you achieve a body shape that is more symmetrical.
Some of my favourite unilateral exercises for the lower body include:
1) Rear foot elevated split squats
2) Reverse lunges
4) Deficit split squats
5) Pistol squats
6) Single leg deadlifts
7) Single leg ball (or roller) hamstring curls
8) Single leg deficit hip thrusts
9) Skater squats
Now that you understand the importance of performing unilateral lower body exercises and have learned some different exercise options, step up your training program and achieve your goals by making unilateral lower body training an integral part of your overall plan. It will pay huge dividends to your overall performance in the gym, sport specific performance, overall health, and aesthetics.